JPH078529B2 - Method for producing biaxially oriented polyester film for magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a biaxially oriented polyester film, and more specifically, the production of a biaxially oriented polyester film which is particularly effective as a magnetic recording medium application. It is about the method.

[Prior Art] Conventionally, a biaxially oriented polyester film for magnetic recording medium containing inert inorganic particles is known from JP-A-59-171623 and JP-A-59-203228. ing. Further, a method of interposing a water film on the surface of the cooling drum and molding the same is known from JP-A-58-63415.

[Problems to be Solved by the Invention] However, in the conventional biaxially oriented polyester film for a magnetic recording medium described above, a film surface is scratched by a roll or the like contacted in a film processing step, for example, a magnetic layer coating, a calendering step, or the like. However, the present situation is that a biaxially oriented polyester film for a magnetic recording medium having a sufficient abrasion resistance has not yet been obtained.

The object of the present invention is to obtain sufficient slip properties, running properties, and smoothness,
Moreover, it is an object of the present invention to provide a method for producing a biaxially oriented polyester film for a magnetic recording medium, which is excellent in abrasion resistance.

[Means for Solving the Problem] The present invention provides a polyester film produced by closely adhering a polyester molten sheet containing 0.01 to 5.0 wt% of inert inorganic particles to the surface of a cooling drum while applying an electrostatic charge. The method for producing a biaxially oriented polyester film for a magnetic recording medium, wherein a liquid film of water is interposed on the surface of the drum.

The polyester in the present invention is a general term for a polymer having an ester bond obtained from polycarboxylic acid and diol by polycondensation, and typical examples thereof include polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, and polycyclohexylenediene. Methylene terephthalate, polyethylene α, β-bis (2
-Chlorphenoxy) ethane 4,4'-dicarboxylate and the like.

Examples of the inert inorganic particles include titanium oxide, calcium carbonate, silica, alumina, talc, clay, barium sulfate, and the like, with alumina, silica, and titanium oxide being particularly preferable.

Here, the particle size ratio of the inert inorganic particles (major axis / minor axis of particle)
It is preferable to use spherical particles having a particle size of 1.0 to 1.3, because it is possible to obtain particles having further excellent wear resistance.

The average particle size of the inert inorganic particles used in the present invention is 10
It is preferably in the range of ~ 500 nm, more preferably 30-450 nm. If it is less than 10 nm, the slip property becomes insufficient, and if it exceeds 500 nm, the abrasion resistance becomes insufficient.

Further, the content of the inert inorganic particles needs to be 0.01 to 5.0 wt%. If the amount is less than the above range, or conversely the amount is more than the above range, abrasion resistance becomes poor, which is not preferable.

In addition to the above-mentioned inert inorganic particles, inert particles of a crosslinked polymer may be contained to the extent that they are normally used.

A method of casting by closely contacting with the surface of a cooling drum while applying an electrostatic charge is already known in Japanese Examined Patent Publication (Kokoku) No. 37-6142.

Although an example of a drum is shown as the cooling body, a movable cooling body such as a belt may be used.

As the surface of the cooling drum, mirror surface chrome plating finish (0.2S
The following) are preferable for the present invention, but the surface may be roughened by etching or sandblasting, or may be hydrophilic if necessary.

Casting methods that apply an electrostatic charge while interposing a liquid film of water on the surface of the cooling drum are BP1140175 and JP-B-63-4492.
It is publicly known in, for example, Japanese Patent Publication.

As a method of interposing a liquid film of water on the surface of the cooling drum,
There is a method of blowing moisture-containing air onto the surface of the cooling drum that is kept below the dew point to cause dew condensation (condensation method), a method of spraying electrostatically charged water vapor, and a method of applying with a seepage roller. However, the apparent thickness d of the liquid film is 3μ
m or less, preferably 1.5 μm or less, more preferably 1.0
The dew condensation method is preferable when the thickness is as thin as μm or less, or when the surface of the cooling drum is plated with specular chrome because a stable liquid film can be obtained. The maximum diameter of water droplets by the condensation method is 50 μm or less, 10
0 to 1000 pieces / 0.1 mm ² is preferable.

Further, it is desirable that the relationship between the apparent thickness d of this average liquid film and the height h of the meniscus formed at the position where the molten sheet and the surface of the cooling drum contact each other is h> d. This apparent water film thickness d is a value obtained by an infrared moisture meter. When h ≦ d, fluctuations in the thickness of the water film formed on the cooling surface are directly transferred to the cast sheet, so stable high-speed casting cannot be performed for a long time. The height h of the meniscus varies depending on the angle at which the molten sheet is in close contact with the drum, the surface roughness of the molten sheet, the surface tension, and the like.

Of course, since the liquid remains unevenly on the drum after the sheet is peeled off from the cooling drum, it is necessary to completely remove the remaining liquid film.Vacuum, air blowing, a combination of both, or a suction roll It is necessary to remove it by the method etc.
If the removal is not sufficient, the coating state of the liquid film as described above cannot be obtained, resulting in surface defects of the film.

Further, in the production method of the present invention, it is necessary to biaxially orient the film obtained by the method described above. Uniaxial or non-oriented is not preferable because the resulting film has poor abrasion resistance. The degree of this orientation is not particularly limited, but it is desirable that the Young's modulus, which is a measure of the degree of molecular orientation of the polymer, is 350 kg / mm ² or more in both the longitudinal direction and the width direction because the abrasion resistance is further improved.

Further, the average projection height of the surface of the film obtained by the production method of the present invention is preferably 20 to 300 nm, preferably 30 to 200 nm, more preferably 35 to 150 nm, and abrasion resistance outside the above range. However, the dubbing resistance is deteriorated, which is not preferable. Further, it is more desirable for the wear resistance that the average protrusion interval is 6 μm or less, preferably 4 μm or less.

That is, a polyester melt sheet containing a specific concentration of inert inorganic particles, by using a specific casting method, smooth and easy slippage, excellent running properties, and biaxial orientation for magnetic recording media excellent in wear resistance A polyester film is obtained, and a film having the above-mentioned characteristics cannot be obtained unless the polyester casting method is used.

That is, the film cast while applying an electrostatic charge on the cooling drum in which the water film was present had low orientation and low crystallinity due to water absorption in its surface layer portion, and it was possible to achieve the above characteristics. .

Further, in order to give the same properties to both surfaces, a roll is arranged on the surface side of the uncooled drum, and the surface temperature of the molten polymer sheet is (melting point −30) to (crystallization peak temperature +5) ° C. It can be achieved by a similar method in which a water film is interposed in part.

Further, the present invention may be in the form of a composite film, in which case the content of the polyester or the specific inert inorganic particles described above may be satisfied in the outer layer portion, and is not affected by the inner layer portion. Absent.

[Effects of the Invention] The following excellent effects are obtained by forming a polyester melt sheet containing a specified content of inert inorganic particles under a specified casting condition.

(1) A film having excellent smoothness, easy slippage, excellent running property, and sufficient abrasion resistance even when contacted with a metal material can be obtained.

(2) A film having excellent dubbing resistance can be obtained.

[Method for evaluating physical properties and method for evaluating effects] (1) Average particle diameter of particles Polyester is removed from the film by a plasma low temperature ashing method (eg, PR-503 type manufactured by Yamato Scientific Co., Ltd.) to expose the particles. As processing conditions, polyester is incinerated but particles are not damaged. SEM this
Observe with a (scanning electron microscope), connect the image of the particles (light and shade of light produced by the particles) to an image analyzer (eg, QTM900 made by Cambridge Instruments), and change the observation point to Numerical processing is performed, and the number average diameter D obtained thereby is taken as the average particle diameter.

D = ΣDi / N Here, Di is the equivalent circle diameter of particles, and N is the number.

(2) Content of inert inorganic particles To 100 g of polyester, add 1.01 of o-chlorophenol
After heating at 120 ℃ for 3 hours, Hitachi Koki Co., Ltd. ultracentrifuge 5
Using 5P-72, centrifugation is performed at 30000 rpm for 40 minutes, and the obtained particles are vacuum dried at 100 ° C. When a fine particle corresponding to a polymer is observed when the fine particles are measured with a scanning differential calorimeter, o-chlorophenol is added to the fine particles, and the mixture is heated and cooled and then centrifuged again. When the melting peak is no longer observed, the fine particles are regarded as precipitated particles. The particle content is defined as the ratio (wt%) of the particles thus separated to the total weight.

(3) Average projection height on the surface A flat surface of the film in a scanning electron microscope (ESM-3200, manufactured by Elionix Co., Ltd.) and a cross-section measuring device (PMS-1, manufactured by Elionix Co., Ltd.) using a two-detector method. The height measurement value of the protrusion when scanning with the height of the
AS2000, manufactured by Carl Zeiss Co., Ltd., to reconstruct the film surface projection image on the image processing device. Next, the equivalent circle diameter is calculated from the area of each protrusion obtained by binarizing the protrusion portion in this surface protrusion image, and this is made the average diameter of the protrusion. In addition, the highest value among the binarized individual projection portions is set as the projection height, and this is obtained for each projection. This measurement place was changed and repeated 500 times, and the height distribution of the measured protrusions was regarded as a normal distribution, and the height distribution was approximated by the least squares method. The magnification of the scanning electron microscope is selected to be a value between 1000 and 8000 times.

(4) Young's modulus Measured at 25 ° C. and 65% RH using an Instron type tensile tester according to the method specified in JIS-Z-1702.

(5) Intrinsic viscosity [η] (unit: dl / g) The value calculated from the following formula from the melt viscosity measured at 25 ° C in orthochlorophenol is used.

η _SP / C = [η] + K [η] ² · C where η _SP = (melt viscosity / solvent viscosity) -1, C is a solvent
Dissolved polymer weight per 100 ml (g / 100 ml, usually 1.
2), K is the Huggins constant (0.343). The solution viscosity and the solvent viscosity were measured using an Ostwald viscometer.

(6) Particle size ratio This is the ratio of the major axis (average value) / minor axis (average value) of the individual particles obtained by the following equation in the measurement of (1) above.

Major axis = ΣD ₁ i / N Minor axis = ΣD ₂ i / ND ₁ i and D ₂ i are the major axis (maximum diameter) and minor axis (shortest diameter) of each particle, and N is the total number.

(7) Abrasion resistance A film slit into a tape having a width of 1/2 inch is run on a guide pin (surface roughness: Ra 100 nm) using a tape running tester (running speed: 500m / min, number of runs: 100 passes, wrapping angle: 180 °).

At this time, the scratches in the film were observed with a microscope, and when two or more scratches were found per tape width, it was judged as poor abrasion resistance, and marked with x, and less than 2 was marked as good with ○. It was

(8) Sliding property The friction coefficient was evaluated by μk. The coefficient of friction μk is obtained by slitting a film into a tape with a width of 1/2 inch, and tape running tester TBT-300 type (manufactured by Yokohama System Research Co., Ltd.)
Was run in an atmosphere of 60% and 80% RH, and the initial coefficient of friction was determined by the following formula (film width was 1/2 inch).

μk = 0.733log (T ₂ / T ₁ ) where T ₁ is the inlet tension and T ₂ is the outlet tension. The guide diameter is 6mmφ, the guide material is SUS27 (surface roughness 0.2S),
The wrap angle is 180 ° and the running speed is 3.3 cm / sec. When μk obtained by this measurement was 0.35 or less, the coefficient of friction was judged to be good (∘), and when it exceeded 0.35, the coefficient of friction was judged to be poor (x). This μk is a critical point that affects the handleability when processing the film for magnetic recording media, capacitor packaging, and the like.

(9) Dubbing resistance A magnetic coating composition having the following composition is applied to a film by a gravure roll, magnetically oriented, and dried. In addition, a small test calendar device (steel roll / nylon roll,
After calendering at a temperature of 70 ° C and a linear pressure of 200 kg / cm (5 stages), cure at 70 ° C for 48 hours. The above raw tape was slit into 1/2 inch to prepare a pancake. A length of 250 m from this pancake was incorporated into a VTR cassette to form a VTR cassette tape.

(Composition of magnetic paint) -Co-containing iron oxide (BET value 50 m ² / g): 100 parts by weight-ESREC A (Sekisui Chemical's vinyl chloride / bimil acetate copolymer): 10 parts by weight-Nipporan 2304 (Nippon Polyurethane) Polyurethane elastomer): 10 parts by weight-Coronate L (polyisocyanate made by Nippon Polyurethane): 5 parts by weight-Lecithin: 1 part by weight-Methyl ethyl ketone: 75 parts by weight-Methyl isobutyl ketone: 75 parts by weight-Toluene: 75 parts by weight-Carbon black : 2 parts by weight Lauric acid: 1.5 parts by weight A home VTR is used for this sample tape to record a 100% chroma signal with a TV test waveform generator (TG7 / U706) made by Shibasoku, and the reproduced signal is used to make Shibasoku colors. Chroma S / N was measured with a video noise measuring device (925D / 1) and was designated as A.
In addition, a tape (mother) on which the same signal as above is recorded is panned on a tape (unrecorded) of the same type of sample by using a magnetic field transfer type video software high-speed printing system (eg, Sprinter manufactured by Sony Magnescale Co., Ltd.) The chroma S / N of the tape after dubbing to the cake was measured in the same manner as above and designated as B. If the decrease in chroma S / N (AB) due to this dubbing is less than 4.0 dB, the dubbing resistance is good.
It is shown with a mark, and when it is 4.0 dB or more, it is shown with a mark x as poor dubbing resistance.

[Examples] The present invention will be described based on Examples.

Examples 1 to 2 and Comparative Examples 1 to 4 Ethylene glycol slurries containing silica particles were prepared and transesterified with dimethyl terephthalate, followed by polycondensation to obtain 1.0 wt% of the particles (Comparative Examples 1 and 2, Pellets of polyethylene terephthalate containing Example 1), 5 wt% (Comparative Example 3, Example 2), and 7 wt% (Comparative Example 4) were made. At this time, the polycondensation time was adjusted so that the intrinsic viscosity was 0.68 (hereinafter referred to as polyester A). Polyester terephthalate having an intrinsic viscosity of 0.62 and containing substantially no inorganic particles was produced by a conventional method, and polyester B
And

Each of these two types of polymers was dried under reduced pressure at 180 ° C. for 3 hours. This polyester A, B is the first
The mixture was supplied to the extruder at the ratio shown in the table, melted at 290 ° C., extruded from a T-die, electrostatically applied on a cooling drum kept at 20 ° C., and cast. On this cooling drum, as shown in Table 1, water film conditions were changed and casting was performed.

This cast sheet is preheated on a roll heated to 90 ° C, stretched 4.2 times in the longitudinal direction, and then stretched 4.3 times in the width direction in a tenter heated to 100 ° C, and then at 210 ° C for 5 seconds. Heat treatment was performed at 165 ° C. for 3 seconds to obtain a biaxially oriented film having a thickness of 15 μm.

The properties of this film are shown in Table 1. A biaxially oriented polyester film for magnetic recording media, which is excellent in abrasion resistance, is obtained by adding a specific amount of inert inorganic particles to polyester and adopting specific casting conditions. It can be seen that

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Claims (1)

[Claims] 1. A method for producing a polyester film, which comprises producing a polyester molten sheet containing 0.01 to 5.0 wt% of inert inorganic particles on the surface of a cooling drum while applying an electrostatic charge to the polyester surface. A method for producing a biaxially oriented polyester film for a magnetic recording medium, which comprises interposing a liquid film of water.